Coated polymeric substrates having improved surface smoothness suitable for use in flexible electronic and opto-electronic devices

ABSTRACT

The use of a coating composition comprising: (a) from about 5 to about 50 weight percent solids, the solids comprising from about 10 to about 70 weight percent silica and from about 90 to about 30 weight percent of a partially polymerized organic silanol of the general formula RSi(OH) 3 , wherein R is selected from methyl and up to about 40% of a group selected from the group consisting of vinyl, phenyl, gamma-glycidoxypropyl, and gamma-methacryloxypropyl, and (b) from about 95 to about 50 weight percent solvent, the solvent comprising from about 10 to about 90 weight percent water and from about 90 to about 10 weight percent lower aliphatic alcohol, wherein the coating composition has a pH of from about 3.0 to about 8.0, for the purpose of improving the surface smoothness of a polymeric substrate, particularly a heat-stabilised, heat-set, oriented polyester substrate, and use of said coated substrate in the manufacture of an electronic or optoelectronic device containing a conjugated conductive polymer.

The present invention relates to a coating composition for improving thesurface smoothness of a substrate on which it is coated, particularly apolymeric substrate suitable for use as a substrate in flexibleelectronic and optoelectronic devices, particularly electroluminescent(EL) display devices, in particular organic light emitting display(OLED) devices.

BACKGROUND OF INVENTION

Electroluminescent (EL) display is a self-emitting display mode whichfeatures excellent visibility (including high brightness, high contrast,very fast response speed and wide viewing angle), an extremely thinprofile and very low power consumption. The EL display device itselfemits light, as do cathode ray tubes (CRT), fluorescent and plasmadisplays. Unlike liquid crystal displays (LCDs), there is no need forbacklighting. The response speed for EL can be as fast as 1000 timesthat for LCD, thus making this mode particularly well suited for usewith moving images. EL displays may be used in a variety ofapplications, including aircraft and ship controls, automobile audioequipment, calculators, mobile telephones, portable computers,instrumentation, factory monitors and electronic medical equipment.Another major application for EL displays is as a light source,particularly as backlighting for small LCD panels in order to renderthem easier to read in low ambient light conditions.

EL displays work by sandwiching a thin film of a phosphorescent or otherelectroluminescent substance between two plates each of which comprisesconductive elements in a predetermined pattern, i.e. electrodes, therebyforming addressable pixels on the display. The electrodes are formed ascoatings either on the electroluminescent substance or on a separatesupport. Where the or each electrode is intended to transmit light, theelectrodes are formed as translucent or transparent coatings, forinstance using transparent conductive metal oxides. Equally, the or eachsupport may be translucent or transparent, as required. Generally, atleast the anode is transparent. The support generally functions both asa base for an electrode and as an insulating layer. The substrate alsoprovides protection against chemical and physical damage in use, storageand transportation. Glass, as well as polymeric film, has been used asthe insulating support.

EL display devices have utilised a variety of cathode materials. Earlyinvestigations employed alkali metals. Other cathode materials includecombinations of metals, such as brass and conductive metal oxides (e.g.,indium tin oxide). A variety of single metal cathodes, such as indium,silver, tin, lead, magnesium, manganese, and aluminum, have also beenused.

Relatively recent discoveries in EL construction include devices whereinthe organic luminescent medium consists of two very thin layers (<1.0 μmin combined thickness) separating the anode and cathode. Representativeof OLED devices are those disclosed in, for instance U.S. Pat. No.4,720,432.

When an electrical current is passed through the conductive elements,the electroluminescent material emits light. EL displays, being anemissive technology, rather than shuttering a light source as per LCDdisplays, are most useful in applications where high visibility in alllight conditions is important.

The development of new, organic electroluminescent materials, which canproduce the three primary colours with very high purity, has madepossible full-colour displays with uniform levels of brightness andlongevity. Polymers having such characteristics can be dissolved insolvents and processed from solution, enabling the printing ofelectronic devices. Conductive conjugated polymers are of particularinterest. As used herein, the term “conjugated conductive polymer”refers to a polymer having pi-electron delocalisation along itsbackbone. Polymers of this type are reviewed by W. J. Feast in Polymer,Vol. 37 (22), 5017-5047, 1996. In a preferred embodiment, the conjugatedconductive polymer is selected from:

-   (i) hydrocarbon conjugated polymers, such as polyacetylenes,    polyphenylenes and poly(p-phenylene vinylenes);-   (ii) conjugated heterocyclic polymers with heteroatoms in the main    chain, such as polythiophenes, polypyrroles and polyanilines; and-   (iii) conjugated oligomers, such as oligothiophenes, oligopyrroles,    oligoanilines, oligophenylenes and oligo(phenylene vinylenes),    containing at least two, preferably at least three, preferably at    least four, preferably at least five, more preferably 6 or more    repeating sub-units.

In addition to use in EL devices, such conjugated conductive polymershave been proposed for use in a variety of other electronic andopto-electronic devices, including photovoltaic cells and semiconductordevices (such as organic field effect transistors, thin film transistorsand integrated circuits generally).

The present invention concerns the insulating and supporting substrateof an electronic or opto-electronic device comprising a conjugatedconductive polymer, including an EL device (particularly an OLED), aphotovoltaic cell and semiconductor devices (such as organic fieldeffect transistors, thin film transistors and integrated circuitsgenerally). The present invention is particularly concerned with thesubstrate of an optoelectronic device, particularly an EL device(particularly an OLED) or a photovoltaic device, and particularly an ELdevice (particularly an OLED).

The substrates can be transparent, translucent or opaque, but aretypically transparent. The substrates are usually required to meetstringent specifications for optical clarity, flatness and minimalbirefringence. Typically, a total light transmission (TLT) of 85% over400-800 nm coupled with a haze of less than 0.7% is desirable fordisplays applications. Surface smoothness and flatness are necessary toensure the integrity of subsequently applied coatings such as theelectrode conductive coating. The substrates should also have goodbarrier properties, i.e. high resistance to gas and solvent permeation.A substrate for use in electronic display applications suitably exhibitswater vapour transmission rates of less than 10⁻⁶ g/m²/day and oxygentransmission rates of less than 10⁻⁵/mL/m²/day. Mechanical propertiessuch as flexibility, impact resistance, hardness and scratch resistanceare also important considerations.

Optical quality glass or quartz has previously been used in electronicdisplay applications as substrates. These materials are able to meet theoptical and flatness requirements and have good thermal and chemicalresistance and barrier properties. However, these materials do not havesome of the desired mechanical properties, most notably low density,flexibility and impact resistance.

In order to improve the mechanical properties, plastics materials havebeen proposed as replacements for glass or quartz sheet. Plasticsubstrates have greater flexibility and improved impact resistance, andare of lighter weight than glass or quartz sheets of equal thickness. Inaddition, a flexible plastic substrate would allow the printing ofelectronic devices, for instance using the conjugated polymers referredto above, onto the substrate in a reel-to-reel process, which wouldreduce cost and allow the manufacture of curved-surface devices.However, the disadvantage of the use of polymeric materials is theirlower chemical resistance and inferior barrier properties. Nevertheless,various barrier coatings have been developed to minimise this problem.These coatings are typically applied in a sputtering process at elevatedtemperatures. A barrier layer may be organic or inorganic, shouldexhibit good affinity for the layer deposited thereupon, and be capableof forming a smooth surface. Materials which are suitable for use toform a barrier layer are disclosed, for instance, in U.S. Pat. No.6,198,217. In order to ensure the integrity of the barrier layer and toprevent “pin-pricks” therein, the surface of the polymeric substratemust exhibit good smoothness.

It is now possible to produce electronic display devices comprisingbarrier-coated polymeric materials which have greater flexibility andimproved impact resistance, and are of lighter weight than glass orquartz sheets of equal thickness. However, some polymeric substratesundergo unacceptable dimensional distortion, such as curl, whensubjected to the processing conditions, particularly elevatedtemperature, during the manufacture of display devices. It is desirableto provide polymeric substrates which exhibit good high-temperaturedimensional stability during the high temperature techniques (such assputtering) used to deposit the barrier layer. One such class ofpolymeric substrates is disclosed in the present Applicant's co-pendingInternational Patent Application PCT/GB2002/04112.

In addition, the surface smoothness of a polymeric substrate is ofteninferior to conventional glass substrates. As noted above, surfacesmoothness is critical in order to ensure the integrity of thesubsequently applied barrier and conductive coatings, and to avoidpin-pricks.

It is an object of this invention to provide a coated polymeric filmsubstrate which overcomes at least one of the aforementioned problems.In particular, it is an object of this invention to provide a coatedpolymeric film substrate having improved surface smoothness,particularly wherein said substrate is suitable for use as a substrate,particularly a flexible substrate, in the manufacture of an electronicor opto-electronic device comprising a conjugated conductive polymer,including an EL device (particularly an OLED), a photovoltaic cell andsemiconductor devices (such as organic field effect transistors, thinfilm transistors and integrated circuits generally). It is a furtherobject to provide a polymeric film having improved surface smoothness,good high-temperature dimensional stability and high optical clarity.

As used herein, a device containing a conjugated conductive polymerpreferably refers to an EL device (particularly an OLED), a photovoltaiccell and semiconductor devices (such as organic field effecttransistors, thin film transistors and integrated circuits generally).As used herein, an opto-electronic device containing a conjugatedconductive polymer preferably refers to an EL device (particularly anOLED) and a photovoltaic device, and particularly an EL device(particularly an OLED). As used herein, the term electronic devicecontaining a conjugated conductive polymer excludes opto-electronicdevices and preferably refers to semiconductor devices such as organicfield effect transistors, thin film transistors and integrated circuitsgenerally, and particularly organic field effect transistors.

SUMMARY OF INVENTION

According to the present invention, there is provided the use of acomposition comprising:

-   (a) from about 5 to about 50 weight percent solids, the solids    comprising from about 10 to about 70 weight percent silica and from    about 90 to about 30 weight percent of a partially polymerized    organic silanol of the general formula RSi(OH)₃, wherein R is    selected from methyl and up to about 40% of a group selected from    the group consisting of vinyl, phenyl, gamma-glycidoxypropyl, and    gamma-methacryloxypropyl, and-   (b) from about 95 to about 50 weight percent solvent, the solvent    comprising from about 10 to about 90 weight percent water and from    about 90 to about 10 weight percent lower aliphatic alcohol,-   wherein the coating composition has a pH of from about 3.0 to about    8.0, preferably from about 3.0 to about 6.5, for the purpose of    improving the surface smoothness of a polymeric substrate when    applied thereto, particularly wherein said use is in the manufacture    of an electronic or optoelectronic device containing a conjugated    conductive polymer which comprises said polymeric substrate, and    particularly wherein said device is an electroluminescent display    device, particularly an OLED device.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 shows a graph illustrating the planarising effect of the presentinvention.

DETAILED DESCRIPTION

Preferably, the pH of the coating composition is less than 6.2,preferably about 6.0 or less. Preferably, the pH of the coatingcomposition is at least 3.5, preferably at least 4.0. In one embodiment,the pH of the coating composition is in the range of from about 4.0 toabout 5.0, preferably from about 4.1 to about 4.8, preferably from about4.3 to about 4.5. The pH of the coating solution can be adjustedaccording to techniques well known to those skilled in the art,including the addition of an acidic or basic solution. For example,suitable acids for the adjustment of the pH include hydrochloric andacetic acids, and suitable bases include sodium hydroxide.

The silica component of the coating compositions may be obtained, forexample, by the hydrolysis of tetraethyl orthosilicate to formpolysilicic acid. The hydrolysis can be carried out using conventionalprocedures, for example, by the addition of an aliphatic alcohol and anacid. Alternatively, the silica used in the instant coating compositionscan be colloidal silica. The colloidal silica should generally have aparticle size of about from 5-25 nm, and preferably about from 7-15 nm.Typical colloidal silicas which can be used in the instant inventioninclude those commercially available as “Ludox SM”, “Ludox HS-30” and“Ludox LS” dispersions (Grace Davison).

The organic silanol component has the general formula RSi(OH)₃. At leastabout 60% of the R groups, and preferably about from 80% to 100% ofthese groups, are methyl. Up to about 40% of the R groups can be higheralkyl or aryl selected from vinyl, phenyl, gamma-glycidoxypropyl, andgamma-methacryloxypropyl.

The combined solids of the coating composition, comprising the silicaand the partially polymerized organic silanol, make up about from 5 to50 weight percent of the total coating composition. Of these solids, thesilica should comprise about from 10 to 70 weight percent, andpreferably about from 20 to 60 weight percent, the complementaryremainder comprising the organic siloxanol. Weight percents of theorganic siloxanol herein are calculated as RSiO_(1.5).

The solvent component of the coating compositions generally comprises amixture of water and one or more lower aliphatic alcohols. The watergenerally comprises about from 10 to 90 weight percent of the solvent,while the lower aliphatic alcohol complementarily comprises about from90 to 10 weight percent. The aliphatic alcohols generally are thosehaving from 1 to 4 carbon atoms, such as methanol, ethanol, n-propanol,iso-propanol, n-butanol, sec-butanol and tertiary butanol.

In addition to the basic solvent components of water and alcohol, thesolvent portion of the compositions can further comprise up to about 10weight percent of a compatible polar solvent such as acetone, ethyleneglycol monoethylether, ethylene glycol monobutylether and diethyleneglycol monoethylether.

Still further components which can be present in the coatingcompositions include curing catalysts. These are preferably present in aconcentration of about from 0.01% to 0.1% based on the total weight ofthe composition, and especially about from 0.01 to 0.3 weight percent.Curing catalysts which may be used in the coating compositions can varywidely. Representative catalysts include the alkali metal salts ofcarboxylic acids such as sodium acetate, potassium acetate, sodiumformate, and potassium formate. Other representative curing catalystswhich can be used include the quaternary ammonium carboxylates, such asbenzyltrimethylammoniun acetate.

Other suitable coating compositions are disclosed in U.S. Pat. Nos.5,069,942 and 5,415,942, the disclosures of which are incorporatedherein by reference. The compositions disclosed therein have a reducedalkali metal cation content (alkali metals had been used to stabilisesilica hydrosols) and exhibit, inter alia, improved adhesion to apolymeric substrate.

The compositions can be prepared by wide variety of techniques,depending on the particular starting materials used. For example,organotrialkoxysilane can be hydrolyzed in the presence of prehydrolyzedpolysilicic acid. Alternatively, organotrialkoxysilane can beprehydrolyzed and then added to a solution of polysilicic acid, oftenresulting in particularly rapid cure times. Still another alternative inthe preparation of these compositions is the cohydrolysis oforganotrialkoxysilane and tetraethyl orthosilicate together.

If a colloidal silica is used as the silica source in the coatingcompositions, the organic silanol can be combined with the silica eitherthrough the prehydrolysis of the organotrialkoxysilane or by hydrolyzingthe organotrialkoxysilane in the presence of acidified colloidal silicadispersion. Still other methods of preparing and combining thecomponents required for the compositions will be evident to thoseskilled in the handling of the individual components.

The coating compositions can be applied using conventional coatingtechniques, including continuous as well as dip coating procedures. Thecoatings are generally applied at a dry thickness of from about 1 toabout 20 microns, preferably from about 2 to 10 microns, andparticularly from about 3 to about 10 microns. The coating compositioncan be applied either “off-line” as a process step distinct from thefilm manufacture, or “in-line” as a continuation of the filmmanufacturing process. In order to improve the surface smoothness of thecoated film, it is desirable to avoid contamination from dust-particlesand the like, and so the coating is preferably conducted off-line in adust-free environment.

The coating compositions, after application to the substrate, can becured at a temperature of from about 20 to about 200° C., preferablyfrom about 20 to about 150° C. While ambient temperatures of 20° C.require cure times of several days, elevated temperatures of 150° C.will cure the coatings in several seconds.

In a preferred embodiment, the substrate is a polyester film, such aspoly(ethylene terephthalate) (PET) or poly(ethylene naphthalate) (PEN),preferably PEN. In a particularly preferred embodiment, the substrate isone described in International Patent Application PCT/GB2002/04112, andthe disclosure therein of such substrates is incorporated herein byreference. Thus, the substrate is preferably a heat-stabilised, heat-setoriented film comprising poly(ethylene naphthalate). Preferably, saidsubstrate has a coefficient of linear thermal expansion (CLTE) withinthe temperature range from −40° C. to +100° C. of less than 40×10⁻⁶/°C., preferably less than 30×10⁻⁶/° C., more preferably less than25×10⁻⁶/° C., more preferably less than 20×10⁻⁶/° C. Preferably, saidsubstrate has a shrinkage at 30 mins at 230° C., measured as definedherein, of less than 1%, preferably less than 0.75%, preferably lessthan 0.5%, preferably less than 0.25%, and more preferably less than0.1%. Preferably, said substrate has a residual dimensional changeΔL_(r) measured at 25° C. before and after heating the film from 8° C.to 200° C. and then cooling to 8° C., of less than 0.75%, preferablyless than 0.5%, preferably less than 0.25%, and more preferably lessthan 0.1%, of the original dimension. In a particularly preferredembodiment, the substrate is a heat-stabilised, heat-set oriented filmcomprising poly(ethylene naphthalate) having the afore-mentionedshrinkage characteristics after 30 min at 230° C., and preferably havingthe afore-mentioned residual dimensional change ΔL_(r) characteristics.The preferred substrates and their preparation are described in moredetail below.

The substrate is self-supporting by which is meant capable ofindependent existence in the absence of a supporting base. The thicknessof the substrate is preferably between about 12 and 300 μm, morepreferably between about 25 and 250 μm, more preferably between about 50and 250 μm.

PEN polyester can be synthesised by conventional methods. A typicalprocess involves a direct esterification or ester exchange reaction,followed by polycondensation. Thus, PEN polyester may be obtained bycondensing 2,5-, 2,6- or 2,7-naphthalenedicarboxylic acid, preferably2,6-naphthalenedicarboxylic acid, or a lower alkyl (up to 6 carbonatoms) diester thereof, with ethylene glycol. Typically,polycondensation includes a solid phase polymerisation stage. The solidphase polymerisation may be carried out on a fluidised bed, e.g.fluidised with nitrogen, or on a vacuum fluidised bed, using a rotaryvacuum drier. Suitable solid phase polymerisation techniques aredisclosed in, for example, EP-A-0419400 the disclosure of which isincorporated herein by reference.

In one embodiment, the PEN is prepared using germanium catalysts whichprovide a polymeric material having a reduced level of contaminants suchas catalyst residues, undesirable inorganic deposits and otherbyproducts of the polymer manufacture. The “cleaner” polymericcomposition promotes improved optical clarity and surface smoothness.

The PEN used to prepare the substrate suitably has a PET-equivalentintrinsic viscosity (IV; measured as described herein) of 0.5-1.5,preferably 0.7-1.5, and in particular 0.79-1.0. An IV of less than 0.5results in a polymeric film lacking desired properties such asmechanical properties whereas an IV of greater than 1.5 is difficult toachieve and would likely lead to processing difficulties of the rawmaterial.

Formation of the substrate may be effected by conventional techniqueswell-known in the art. Conveniently, formation of the substrate iseffected by extrusion, in accordance with the procedure described below.In general terms the process comprises the steps of extruding a layer ofmolten polymer, quenching the extrudate and orienting the quenchedextrudate in at least one direction.

The substrate may be uniaxially-oriented, but is preferablybiaxially-oriented. Orientation may be effected by any process known inthe art for producing an oriented film, for example a tubular or flatfilm process. Biaxial orientation is effected by drawing in two mutuallyperpendicular directions in the plane of the film to achieve asatisfactory combination of mechanical and physical properties.

In a tubular process, simultaneous biaxial orientation may be effectedby extruding a thermoplastics polyester tube which is subsequentlyquenched, reheated and then expanded by internal gas pressure to inducetransverse orientation, and withdrawn at a rate which will inducelongitudinal orientation.

In the preferred flat film process, the substrate-forming polyester isextruded through a slot die and rapidly quenched upon a chilled castingdrum to ensure that the polyester is quenched to the amorphous state.Orientation is then effected by stretching the quenched extrudate in atleast one direction at a temperature above the glass transitiontemperature of the polyester. Sequential orientation may be effected bystretching a flat, quenched extrudate firstly in one direction, usuallythe longitudinal direction, i.e. the forward direction through the filmstretching machine, and then in the transverse direction. Forwardstretching of the extrudate is conveniently effected over a set ofrotating rolls or between two pairs of nip rolls, transverse stretchingthen being effected in a stenter apparatus. Alternatively, orientationmay be generated in the extruded film by way of simultaneous stretching.Here, the film is stretched in the longitudinal and transversedirections in what is essentially the same stage of the process, in thestenter oven. For both routes of sequential and simultaneous stretching,the extent of stretching is determined partly by the nature of thepolyester. However the film is usually stretched so that the dimensionof the oriented film is from 2 to 5, more preferably 2.5 to 4.5 timesits original dimension in each direction of stretching. Typically,stretching is effected at temperatures in the range of 70 to 150° C.,typically 70 to 140° C. Greater draw ratios (for example, up to about 8times) may be used if orientation in only one direction is required. Itis desired to obtain a film having balanced properties, which may beachieved for example controlling the stretching conditions in themachine and transverse directions.

The stretched film is dimensionally stabilised by heat-setting underdimensional restraint at a temperature above the glass transitiontemperature of the polyester but below the melting temperature thereof,to induce crystallisation of the polyester, as described in GB-A-838708.The tension of dimensional restraint is generally in the range of about19 to about 75 kg/m, preferably about 45 to about 50 kg/m of film widthwhich, for a film having a width of about 2.6 m is a tension in therange of about 50 to about 190 kg, preferably in the range of 120-130kg. The actual heat-set temperature and time will vary depending on thecomposition of the film but should be selected so as not tosubstantially degrade the tear resistant properties of the film. Withinthese constraints, a heat-set temperature of about 135° to 250° C. isgenerally desirable, more preferably 235-240° C. The duration of heatingwill depend on the temperature used but is typically in the range of 5to 40 secs, preferably 8 to 30 secs.

The film is then further heat-stabilised by heating it under low tension(i.e. with the minimum possible dimensional restraint) at a temperatureabove the glass transition temperature of the polyester but below themelting point thereof, in order to allow the majority of the inherentshrinkage in the film to occur (relax out) and thereby produce a filmwith very low residual shrinkage and consequently high dimensionalstability. The tension experienced by the film during thisheat-stabilisation step is typically less than 5 kg/m, preferably lessthan 3.5 kg/m, more preferably in the range of from 1 to about 2.5 kg/m,and typically in the range of 1.5 to 2 kg/m of film width. There is noincrease in the transverse dimension of the film during theheat-stabilisation step. The temperature to be used for the heatstabilisation step can vary depending on the desired combination ofproperties from the final film, with a higher temperature giving better,i.e. lower, residual shrinkage properties. A temperature of 135° C. to250° C. is generally desirable, preferably 190 to 250° C., morepreferably 200 to 230° C., and more preferably at least 215° C.,typically 215 to 230° C. The duration of heating will depend on thetemperature used but is typically in the range of 10 to 40 sec, with aduration of 20 to 30 secs being preferred. This heat stabilisationprocess can be carried out by a variety of methods, including flat andvertical configurations and either “off-line” as a separate process stepor “in-line” as a continuation of the film manufacturing process. In oneembodiment, heat stabilisation is conducted “off-line”.

The substrate may comprise one or more discrete layers. The compositionof the respective layers may be the same or different. For instance, thesubstrate may comprise one, two, three, four or five or more layers andtypical multi-layer structures may be of the AB, ABA, ABC, ABAB, ABABAor ABCBA type. Preferably, the substrate comprises only one layer. Wherethe substrate comprises more than one layer, preparation of thesubstrate is conveniently effected by coextrusion, lamination orcasting, in accordance with conventional techniques well-known in theart.

The substrate may conveniently contain any of the additivesconventionally employed in the manufacture of polymeric films. Thus,agents such as cross-linking agents, dyes, pigments, voiding agents,lubricants, anti-oxidants, radical scavengers, UV absorbers, thermalstabilisers, flame retardants, anti-blocking agents, surface activeagents, slip aids, optical brighteners, gloss improvers, prodegradents,viscosity modifiers and dispersion stabilisers may be incorporated asappropriate. The components of the substrate may be mixed together in aconventional manner.

In a preferred embodiment, the film described herein is optically clear,preferably having a % of scattered visible light (haze) of <3.5%,preferably <2%, more preferably <1.5%, more preferably ≦1%, andparticularly less than 0.7%, measured according to the standard ASTM D1003. In one embodiment, the haze is in the range of 0.6 to 1.0%.Preferably the total light transmission (TLT) in the range of 400-800 nmis at least 75%, preferably at least 80%, and more preferably at least85%, measured according to the standard ASTM D 1003. In this embodiment,filler is typically present in only small amounts, generally notexceeding 0.5% and preferably less than 0.2% by weight of a given layer.

In an alternative embodiment, the substrate is opaque and highly filled,preferably exhibiting a Transmission Optical Density (TOD) (SakuraDensitometer; type PDA 65; transmission mode) in the range from 0.1 to2.0, more preferably 0.2 to 1.5, more preferably from 0.25 to 1.25, morepreferably from 0.35 to 0.75 and particularly 0.45 to 0.65. The film isconveniently rendered opaque by incorporation into the polymer blend ofan effective amount of an opacifying agent. Suitable opacifying agentsinclude an incompatible resin filler, a particulate inorganic filler ora mixture of two or more such fillers. Preferred particulate inorganicfillers include titanium dioxide and silica. Suitable incompatibleresins include polyamides and olefin polymers, particularly a homo- orco-polymer of a mono-alpha-olefin containing up to 6 carbon atoms in itsmolecule. The amount of filler present in a given layer is preferably inthe range from 1% to 30%, more preferably 3% to 20%, particularly 4% to15%, and especially 5% to 10% by weight, based on the weight of thelayer polymer.

Prior to coating the substrate, it may be desirable to pretreat thesubstrate to promote adhesion of the coating. Various adhesion promotingtechniques known to those skilled in the art can be used, such as flametreating, corona discharge, and/or resin coating.

In a preferred embodiment, the substrate is coated with a primer layerto improve adhesion of the substrate to the planarising coatingcomposition. The primer layer may be any suitable adhesion-promotingpolymeric composition known in the art, including polyester and acrylicresins. The primer composition may also be a mixture of a polyesterresin with an acrylic resin. Acrylic resins may optionally compriseoxazoline groups and polyalkylene oxide chains. The polymer(s) of theprimer composition is/are preferably water-soluble or water-dispersible.

Polyester primer components include those obtained from the followingdicarboxylic acids and diols. Suitable di-acids include terephthalicacid, isophthalic acid, phthalic acid, phthalic anhydride,2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid,adipic acid, sebacic acid, trimellitic acid, pyromellitic acid, a dimeracid, and 5-sodium sulfoisophthalic acid. A copolyester using two ormore dicarboxylic acid components is preferred. The polyester mayoptionally contain a minor amount of an unsaturated di-acid componentsuch as maleic acid or itaconic acid or a small amount of ahydroxycarboxylic acid component such as p-hydroxybenzoic acid. Suitablediols include ethylene glycol, 1,4-butanediol, diethylene glycol,dipropylene glycol, 1,6-hexanediol, 1,4-cyclohexanedimethylol, xyleneglycol, dimethylolpropane, poly(ethylene oxide)glycol, andpoly(tetramethylene oxide)glycol. The glass transition point of thepolyester is preferably 40 to 100° C., further preferably 60 to 80° C.Suitable polyesters include copolyesters of PET or PEN with relativelyminor amounts of one or more other dicarboxylic acid comonomers,particularly aromatic di-acids such as isophthalic acid and sodiumsulphoisophthalic acid, and optionally relatively minor amounts of oneor more glycols other than ethylene glycol, such as diethylene glycol.

In one embodiment, the primer layer comprises an acrylate ormethacrylate polymer resin. The acrylic resin may comprise one or moreother comonomers. Suitable comonomers include alkyl acrylates, alkylmethacrylates (where the alkyl group is preferably methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl,cyclohexyl or the like); hydroxy-containing monomers such as2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropylacrylate, and 2-hydroxypropyl methacrylate; epoxy group-containingmonomers such as glycidyl acrylate, glycidyl methacrylate, and allylglycidyl ether; carboxyl group or its salt-containing monomers, such asacrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaricacid, crotonic acid, styrenesulfonic acid and their salts (sodium salt,potassium salt, ammonium salt, quaternary amine salt or the like); amidegroup-containing monomers such as acrylamide, methacrylamide, anN-alkylacrylamide, an N-alkylmethacrylamide, an N,N-dialkylacrylamide,an N,N-dialkyl methacrylate (where the alkyl group is preferablyselected from those described above), an N-alkoxyacrylamide, anN-alkoxymethacrylamide, an N,N-dialkoxyacrylamide, anN,N-dialkoxymethacrylamide (the alkoxy group is preferably methoxy,ethoxy, butoxy, isobutoxy or the like), acryloylmorpholine,N-methylolacrylamide, N-methylolmethacrylamide, N-phenylacrylamide, andN-phenylmethacrylamide; acid anhydrides such as maleic anhydride anditaconic anhydride; vinyl isocyanate, allyl isocyanate, styrene,α-methylstyrene, vinyl methyl ether, vinyl ethyl ether, avinyltrialkoxysilane, a monoalkyl maleate, a monoalkyl fumarate, amonoalkyl itaconate, acrylonitrile, methacrylonitrile, vinylidenechloride, ethylene, propylene, vinyl chloride, vinyl acetate, andbutadiene. In a preferred embodiment, the acrylic resin is copolymerisedwith one or more monomer(s) containing oxazoline groups and polyalkyleneoxide chains.

The oxazoline group-containing monomer includes 2-vinyl-2-oxazoline,2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline,2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and2-isopropenyl-5-methyl-2-oxazoline. One or more comonomers may be used.2-Isopropenyl-2-oxazoline is preferred.

The polyalkylene oxide chain-containing monomer includes a monomerobtained by adding a polyalkylene oxide to the ester portion of acrylicacid or methacrylic acid. The polyalkylene oxide chain includespolymethylene oxide, polyethylene oxide, polypropylene oxide, andpolybutylene oxide. It is preferable that the repeating units of thepolyalkylene oxide chain are 3 to 100.

Where the primer composition comprises a mixture of polyester andacrylic components, particularly an acrylic resin comprising oxazolinegroups and polyalkylene oxide chains, it is preferable that the contentof the polyester is 5 to 95% by weight, preferably 50 to 90% by weight,and the content of the acrylic resin is 5 to 90% by weight, preferably10 to 50% by weight.

Other suitable acrylic resins include:

-   (i) a copolymer of (a) 35 to 40 mole % alkyl acrylate, (b) 35 to 40%    alkyl methacrylate, (c) 10 to 15 mole % of a comonomer containing a    free carboxyl group such as itaconic acid, and (d) 15 to 20 mole %    of an aromatic sulphonic acid and/or salt thereof such as p-styrene    sulphonic acid, an example of which is a copolymer comprising ethyl    acrylate/methyl methacrylate/itaconic acid/p-styrene sulphonic acid    and/or a salt thereof in a ratio of 37.5/37.5/10/15 mole %, as    disclosed in EP-A-0429179 the disclosure of which is incorporated    herein by reference; and-   (ii) an acrylic and/or methacrylic polymeric resin, an example of    which is a polymer comprising about 35 to 60 mole % ethyl acrylate,    about 30 to 55 mole % methyl methacrylate and about 2 to 20 mole %    methacrylamide, as disclosed in EP-A-0408197 the disclosure of which    is incorporated herein by reference.

The primer or adherent layer may also comprise a cross-linking agentwhich improves adhesion to the substrate and should also be capable ofinternal cross-linking. Suitable cross-linking agents include optionallyalkoxylated condensation products of melamine with formaldehyde. Theprimer or adherent layer may also comprise a cross-linking catalyst,such as ammonium sulphate, to facilitate the cross-linking of thecross-linking agent. Other suitable cross-linking agents and catalystsare disclosed in EP-A-0429179, the disclosures of which are incorporatedherein by reference.

The primer coating may also contain a minor amount of one or more typesof filler particles in order to assist in the handling of the film,particularly wherein the planarising coating composition is coatedoff-line. In one embodiment, the filler may comprise silica, and/orcomposite inorganic particles of silica with titania. The averageparticle diameter of the fine particles is preferably ranged from 40 to120 nm. The primer coating should not be detrimental to the opticalqualities of the substrate as described herein.

The primer layer may optionally contain an aliphatic wax to improve thehandling and slip properties of the film surface. The content of thealiphatic wax is preferably at least 0.5% by weight in order to obtainthe improvement, and preferably is 0.5 to 30%, further preferably 1 to10% by weight. It is undesirable that the content exceeds 30% by weight,because the adhesion of the primer layer to the polyester film substrateand the subsequently-applied layer may deteriorate. Suitable aliphaticwax include vegetable waxes such as carnauba wax, candelilla wax, ricewax, Japan tallow, jojoba oil, palm wax, rosin-modified wax, ouricurywax, sugarcane wax, esparto wax, and bark wax; animal waxes such asbeeswax, lanolin, spemmaceti, insect wax, and shellac wax; mineral waxessuch as montan wax, ozokerite, and ceresin wax; petroleum waxes such asparaffin wax, microcrystalline wax; and petrolatum, and synthetichydrocarbon waxes such as Fischer-Tropsch wax, polyethylene wax,polyethylene oxide wax, polypropylene wax, and polypropylene oxide wax.Carnauba wax, paraffin wax and polyethylene wax are preferred. It ispreferable to use the waxes as water dispersions.

The primer coating may also comprise an anti-static agent and/or awetting agent, as known in the art.

A further suitable primer is disclosed in U.S. Pat. No. 3,443,950, thedisclosure of which is incorporated herein by reference.

The coating of the primer layer onto the substrate may be performedin-line or off-line, but is preferably performed “in-line”, andpreferably between the forward and sideways stretches of a biaxialstretching operation.

Once the coating composition has been coated onto the substrate, thecoated substrate is then ready for further processing and coating inpreparation for its end-use. In the manufacture of the electronic andopto-electronic devices mentioned herein, the film is then coated with abarrier layer, as noted above. Such coatings are known in the art andare typically applied in a sputtering process at elevated temperatures.Materials which are suitable for use to form a barrier layer aredisclosed, for instance, in U.S. Pat. No. 6,198,217. An organic barrierlayer may be formed from, for instance, photocurable monomers oroligomers, or thermoplastic resins. Photocurable monomers or oligomersshould have low volatility and high melting points. Examples of suchmonomers include trimethylol acrylates such as trimethylolpropanetriacrylate, ditrimethylolpropane tetraacrylate and the like; long-chainacrylates such as 1,6-hexanediol diacrylate, 1,6-hexanedioldimethacrylate and the like; and cyclohexyl acrylates such asdicyclopentenyloxyethyl acrylate, dicyclopentenyloxy acrylate,cyclohexyl methacrylate and the like. Examples of such oligomers includeacrylate oligomers, epoxy acrylate oligomers, urethane acrylateoligomers, ether acrylate oligomers, and the like. Photoinitiators, suchas benzoin ethers, benzophenones, acetophenones, ketals and the like,may be used to cure the resin. Examples of suitable thermoplastic resinsinclude polyethylene, polymethyl methacrylate, polyethyleneterephthalate and the like. These organic materials may be applied byany conventional technique known in the art, such as by vacuumdeposition. An inorganic barrier layer should be made of a materialwhich exhibits low moisture permeability and is stable against moisture.Examples include oxides such as SiO₂, SiO, GeO, Al₂O₃ and the like,nitrides such as TiN, Si₃N₄ and the like, and metals such as Al, Ag, Au,Pt, Ni and the like. The inorganic material may be applied using avapour phase technique such as vacuum deposition, sputtering and thelike under standard conditions. A barrier layer can itself comprise oneor more discrete layers, and may comprise one or more organic layer(s)and one or more inorganic layer(s).

In a preferred embodiment, the barrier layer is a layer which reducesthe water vapour transmission rate of the substrate in an optoelectronicdevice to less than 10⁻⁶ g/m²/day and the oxygen transmission rate toless than 10⁻⁵/mL/m²/day. In an alternative embodiment, the barrierlayer is a layer which reduces the water vapour transmission rate of thesubstrate in an electronic device to less than 10⁻² g/m²/day (preferablyless than 10⁻⁶ g/m²/day) and the oxygen transmission rate to less than10⁻³/mL/m²/day (preferably less than 10⁻⁵/mL/m²/day).

Once the barrier layer has been deposited, subsequent layers, includingthe electrode and conductive conjugated polymer, may be applied inaccordance with conventional manufacturing techniques known in the art.The electrode may be any suitable electrode known in the art, forinstance an electrode selected from those mentioned herein. In oneembodiment, the electrode is a conductive metal oxide, preferably indiumtin oxide.

The electronic and opto-electronic devices referred to generally hereincomprise one (or more) layers of conductive conjugated polymer, two ormore electrodes, and one or more substrate layers.

In one embodiment of the invention, the term electroluminescent displaydevice, particularly an organic light emitting display (OLED) device,refers to a display device comprising a layer of light-emittingconductive conjugated polymeric material disposed between two layerseach of which comprises an electrode, wherein the resultant compositestructure is disposed between two substrate (or support or cover)layers.

In one embodiment of the invention, the term photovoltaic cell refers toa device comprising a layer of conductive conjugated polymeric materialdisposed between two layers each of which comprises an electrode,wherein the resultant composite structure is disposed between twosubstrate (or support or cover) layers.

In one embodiment of the invention, the term transistor refers to adevice comprising at least one layer of conductive conjugated polymer, agate electrode, a source electrode and a drain electrode, and one ormore substrate layers.

According to a further aspect of the invention, there is provided acomposite film comprising a substrate, preferably a heat-stabilised,heat-set, oriented polyester substrate, and a coating layer, wherein thecoating layer is derived from the coating composition described herein,and wherein the surface of said coated substrate exhibits an Ra value,as measured herein, of less than 0.7 nm, preferably less than 0.6 nm,preferably less than 0.5 nm, preferably less than 0.4 mm, preferablyless than 0.3 nm, and ideally less than 0.25 nm, and/or an Rq value, asmeasured herein, of less than 0.9 nm, preferably less than 0.8 nm,preferably less than 0.75 nm, preferably less than 0.65 nm, preferablyless than 0.6 nm, preferably less than 0.50 nm, preferably 0.45 nm orlower, preferably less than 0.35 nm, and ideally less than 0.3 nm.

According to a further aspect of the invention there is provided acomposite film comprising a heat-stabilised, heat-set, orientedsubstrate comprising poly(ethylene naphthalate), and a coating layer;preferably wherein said substrate has one or more of (i) theafore-mentioned coefficient of linear thermal expansion (CLTE)characteristics, and/or (ii) the afore-mentioned shrinkagecharacteristics, and/or (iii) the afore-mentioned residual dimensionalchange ΔL_(r) characteristics; and wherein said coating is sufficient toimprove the surface smoothness of said substrate such that the Ra valueand/or the Rq value satisfy the thresholds described hereinabove. In apreferred embodiment of this aspect of the invention, the coatingcomprises a polysiloxane derived from a coating composition comprising:

-   (a) about from 5 to 50 weight percent solids, the solids comprising    about from 10 to 70 weight percent silica and about from 90 to 30    weight percent of a partially polymerized organic silanol of the    general formula RSi(OH)₃, wherein R is selected from methyl and up    to about 40% of a group selected from the group consisting of vinyl,    phenyl, gamma-glycidoxypropyl, and gamma-methacryloxypropyl, and-   (b) about from 95 to 50 weight percent solvent, the solvent    comprising about from 10 to 90 weight percent water and about from    90 to 10 weight percent lower aliphatic alcohol, wherein the coating    composition has a pH of about from 3.0 to 8.0.

In one embodiment, said coated substrate comprises said substrate layer,and on both surfaces thereof said coating layer. A symmetrical film ofthis type is particularly useful in providing a dimensionally stablefilm in which film curl during subsequent processing is minimised oravoided.

In one embodiment, said coated substrate is one which is obtainable bythe method described hereinbelow.

According to a further aspect of the present invention, there isprovided a composite film comprising a substrate layer as describedherein and on a surface thereof a planarising coating layer as describedherein and on a surface of the coating layer a barrier layer asdescribed herein, and optionally further comprising an electrode layeron at least part of the surface of the barrier layer, and optionallyfurther comprising a layer of conjugated conductive polymer. In oneembodiment, the composite film comprises said substrate layer, and onboth surfaces thereof said planarising coating layer, and on bothsurfaces of said coated substrate a barrier layer.

According to a further aspect of the invention there is provided amethod of manufacture of a coated polymeric film which comprises thesteps of:

-   (i) forming a layer comprising poly(ethylene naphthalate);-   (ii) stretching the layer in at least one direction;-   (iii) heat-setting under dimensional restraint at a tension in the    range of about 19 to about 75 kg/m, preferably about 45 to about 50    kg/m of film width, at a temperature above the glass transition    temperature of the polyester but below the melting temperature    thereof;-   (iv) heat-stabilising under low tension, preferably at a tension of    less than 5 kg/m, more preferably at a tension of less than 3.5    kg/m, more preferably at a tension in the range of 1.0 to 2.5 kg/m,    and typically at a tension in the range of 1.5 to 2.0 kg/m of film    width, and at a temperature above the glass transition temperature    of the polyester but below the melting temperature thereof; and-   (v) applying a planarising coating composition thereto preferably    such that the Ra value and/or Rq value satisfy the thresholds    described hereinabove.

According to a further aspect of the present invention, there isprovided a method for the manufacture of an electronic oropto-electronic device containing a conjugated conductive polymer and asubstrate as described herein, said method comprising the steps of:

-   (i) forming a layer comprising poly(ethylene naphthalate);-   (ii) stretching the layer in at least one direction;-   (iii) heat-setting under dimensional restraint at a tension in the    range of about 19 to about 75 kg/m, preferably about 45 to about 50    kg/m of film width, at a temperature above the glass transition    temperature of the polyester but below the melting temperature    thereof;-   (iv) heat-stabilising under low tension, preferably at a tension of    less than 5 kg/m, more preferably at a tension of less than 3.5    kg/m, more preferably at a tension in the range of 1.0 to 2.5 kg/m,    and typically at a tension in the range of 1.5 to 2.0 kg/m of film    width, and at a temperature above the glass transition temperature    of the polyester but below the melting temperature thereof;-   (v) applying a planarising coating composition thereto preferably    such that the Ra value and/or Rq value satisfy the thresholds    described hereinabove; and-   (vi) providing the coated, heat-stabilised, heat-set, oriented film    as a substrate in the device.

Steps in the manufacture of the electronic or optoelectronic device mayfurther comprise providing on a surface of the coated substrate abarrier layer, providing an electrode by applying a conductive materialonto at least part of the barrier layer; and providing a layer of aconductive conjugated polymer.

As used herein, the term “planarising coating composition” refers to apolymeric coating composition which increases the surface smoothness ofa substrate when applied thereto, preferably such that the surfacesmoothness is improved such that the Ra value, as measured herein, isless than 0.7 nm, preferably less than 0.6 nm, preferably less than 0.5nm, preferably less than 0.4 nm, preferably less than 0.3 nm, andideally less than 0.25 nm, and preferably such that the Rq value, asmeasured herein, is less than 0.9 nm, preferably less than 0.8 nm,preferably less than 0.75 nm, preferably less than 0.65 nm, preferablyless than 0.6 nm, preferably less than 0.50 nm, preferably 0.45 nm orlower, preferably less than 035 nm, and ideally less than 0.3 nm. In apreferred embodiment, the planarising coating composition comprises apolysiloxane derived from a composition comprising:

-   (a) about from 5 to 50 weight percent solids, the solids comprising    about from 10 to 70 weight percent silica and about from 90 to 30    weight percent of a partially polymerized organic silanol of the    general formula RSi(OH)₃, wherein R is selected from methyl and up    to about 40% of a group selected from the group consisting of vinyl,    phenyl, gamma-glycidoxypropyl, and gamma-methacryloxypropyl, and-   (b) about from 95 to 50 weight percent solvent, the solvent    comprising about from 10 to 90 weight percent water and about from    90 to 10 weight percent lower aliphatic alcohol, wherein the coating    composition has a pH of about from 3.0 to 8.0.

According to a further aspect of the invention, there is provided theuse of a planarising coating composition in the manufacture of anelectronic or opto-electronic containing a conjugated conductive polymerand which comprises a polymeric substrate, for the purpose of improvingthe surface smoothness of said polymeric substrate.

The following test methods may be used to determine certain propertiesof the polymeric film:

-   (i) the clarity of the film may be evaluated by measuring total    luminance transmission (TLT) and haze (% of scattered transmitted    visible light) through the total thickness of the film using a    Gardner XL 211 hazemeter in accordance with ASTM D-1003-61.-   (ii) Transmission Optical Density (TOD) of the film may be measured    using a Macbeth Densitometer TR 927 (Dent & Woods Ltd, Basingstoke,    UK) in transmission mode.-   (iii) Dimensional stability may be assessed in terms of either (a)    the coefficient of linear thermal expansion (CLTE) or (b) a    temperature cycling method wherein the residual change in length    along a given axis is measured after heating the film to a given    temperature and subsequently cooling the film.    -   Both methods of measurements were conducted using a        Thermomechanical Analyser PE-TMA-7 (Perkin Elmer) calibrated and        checked in accordance with known procedures for temperature,        displacement, force, eigendeformation, baseline and furnace        temperature alignment. The films were examined using extension        analysis clamps. The baseline required for the extension clamps        was obtained using a very low coefficient of expansion specimen        (quartz) and the CLTE precision and accuracy (dependent on        post-scan baseline subtraction) was assessed using a standard        material, e.g. pure aluminium foil, for which the CLTE value is        well known. The specimens, selected from known axes of        orientation within the original film samples, were mounted in        the system using a clamp separation of approx. 12 mm and        subjected to an applied force of 75 mN over a 5 mm width. The        applied force was adjusted for changes in film thickness, i.e.        to ensure consistent tension, and the film was not curved along        the axis of analysis. Specimen lengths were normalised to the        length measured at a temperature of 23° C.    -   In the CLTE test method (a), specimens were cooled to 8° C.,        stabilised, then heated at 5° C./min from 8° C. to +240° C. The        CLTE values (α) were derived from the formula:        α=ΔL/(L×(T ₂ −T ₁))    -   where ΔL is the measured change in length of the specimen over        the temperature range (T₂−T₁), and L is the original specimen        length at 23° C. CLTE values are considered reliable up to the        temperature of the Tg (120° C.).    -   The data can be plotted as a function of the % change in        specimen length with temperature, normalised to 23° C.    -   In the temperature cycling test method (b), a procedure similar        to that of method (a) was used wherein the temperature was        cycled between 8° C. and several elevated temperatures. Thus,        film samples were heated from 8° C. to 140° C., 160° C., 180° C.        or 200° C. and then cooled to 8° C. The length along each of the        transverse and machine directions was measured at 25° C. before        and after this heat treatment and the change in length ΔL_(r)        calculated as percentage of the original length.-   (iv) Intrinsic Viscosity (IV)    -   The IV was measured by melt viscometry, using the following        procedure. The rate of flow pre-dried extrudate through a        calibrated die at known temperature and pressure is measured by        a transducer which is linked to a computer. The computer        programme calculates melt viscosity values (log₁₀ viscosity) and        equivalent IVs from a regression equation determined        experimentally. A plot of the IV against time in minutes is made        by the computer and the degradation rate is calculated. An        extrapolation of the graph to zero time gives the initial IV and        equivalent melt viscosity. The die orifice diameter is 0.020        inches, with a melt temperature of 284° C. for IV up to 0.80,        and 295° C. for IV>0.80.-   (v) Shrinkage    -   Shrinkage at a given temperature is measured by placing the        sample in a heated oven for a given period of time. The %        shrinkage is calculated as the % change of dimension of the film        in a given direction before and after heating.-   (vi) Surface Smoothness    -   Surface smoothness was measured using conventional        non-contacting, white-light, phase-shifting interferometry        techniques, which are well-known in the art. The instrument used        was a Wyko NT3300 surface profiler using a light source of        wavelength 604 nm. With reference to the WYKO Surface Profiler        Technical Reference Manual (Veeco Process Metrology, Arizona,        US; June 1998; the disclosure of which is incorporated herein by        reference), the characterising data obtainable using the        technique include:    -   Averaging Parameter—Roughness Average (Ra): the arithmetic        average of the absolute values of the measured height deviations        within the evaluation area and measured from the mean surface.    -   Averaging Parameter—Root Mean Square Roughness (Rq): the root        mean square average of the measured height deviations within the        evaluation area and measured from the mean surface.    -   Extreme Value Parameter—Maximum Profile Peak Height (Rp): the        height of the highest peak in the evaluation area, as measured        from the mean surface.    -   Averaged Extreme Value Parameter—Average Maximum Profile Peak        Height (Rpm): the arithmetic average value of the ten highest        peaks in the evaluation area.    -   Extreme Peak Height Distribution: a number distribution of the        values of Rp of height greater than 200 nm.    -   Surface Area Index: a measure of the relative flatness of a        surface.    -   The roughness parameters and peak heights are measured relative        to the average level of the sample surface area, or “mean        surface”, in accordance with conventional techniques. (A        polymeric film surface may not be perfectly flat, and often has        gentle undulations across its surface. The mean surface is a        plane that runs centrally through undulations and surface height        departures, dividing the profile such that there are equal        volumes above and below the mean surface.)    -   The surface profile analysis is conducted by scanning discrete        regions of the film surface within the “field of view” of the        surface profiler instrument, which is the area scanned in a        single measurement A film sample may be analysed using a        discrete field of view, or by scanning successive fields of view        to form an array.    -   The analyses conducted herein utilised the full resolution of        the Wyko NT3300 surface profiler, in which each field of view        comprises 480×736 pixels.    -   For the measurement of Ra and Rq, the resolution was enhanced        using an objective lens having a 50-times magnification. The        resultant field of view has dimensions of 90 μm×120 μm, with a        pixel size of 0.163 μm.    -   For the measurement of Rp and Rpm, the field of view is        conveniently increased using an objective lens having a 10-times        magnification in combination with a “0.5-times field of view of        multiplier” to give a total magnification of 5-times. The        resultant field of view has dimensions of 0.9 mm×1.2 mm, with a        pixel size of 1.63 μm. Preferably Rp is less than 100 nm, more        preferably less than 60 nm, more preferably less than 50 nm,        more preferably less than 40 nm, more preferably less than 30        nm, and more preferably less than 20 nm.    -   For the measurement of Ra and Rq herein, the results of five        successive scans over the same portion of the surface area are        combined to give an average value. The data presented below in        respect of Rp are an average value from 100 measurements. The        measurements were conducted using a modulation threshold        (signal:noise ratio) of 10%, i.e. data points below the        threshold are identified as bad data.    -   The surface topography can also be analysed for the presence of        extreme peaks having a height of greater than 200 nm. In this        analysis, a series of measurements of Rp are taken with a pixel        size of 1.63 μm over a total area of 5 cm². The results may be        presented in the form of a histogram in which the data-points        are assigned to pre-determined ranges of peak heights, for        instance wherein the histogram has equally-spaced channels along        the x-axis of channel width 25 nm. The histogram may be        presented in the form of a graph of peak count (y axis) versus        peak height (x axis); see for instance FIG. 1. The number of        surface peaks in the range 300 to 600 nm per 5 cm² area, as        determined from Rp values, may be calculated, and designated as        N(300-600). The use of a planarising coating according to the        present invention preferably results in a reduction of        N(300-600), such that the reduction F, which is the ratio of        N(300-600) before and after application of the planarising        coating, is at least 5, preferably at least 15, and more        preferably at least 30. Preferably, the N(300-600) value of the        planarised film (after coating) is less than 50, preferably less        than 35, preferably less than 20, preferably less than 10, and        preferably less than 5 peaks per 5 cm² area.    -   The Surface Area Index is calculated from the “3-dimensional        surface area” and the “lateral surface area” as follows. The        “3-dimensional (3-D) surface area” of a sample area is the total        exposed 3-D surface area including peaks and valleys. The        “lateral surface area” is the surface area measured in the        lateral direction. To calculate the 3-D surface area, four        pixels with surface height are used to generate a pixel located        in the centre with X, Y and Z dimensions. The four resultant        triangular areas are then used to generate approximate cubic        volume. This four-pixel window moves through the entire        data-set. The lateral surface area is calculated by multiplying        the number of pixels in the field of view by the XY size of each        pixel. The surface area index is calculated by dividing the 3-D        surface area by the lateral area, and is a measure of the        relative flatness of a surface. An index which is very close to        unity describes a very flat surface where the lateral (XY) area        is very near the total 3-D area (XYZ).    -   A Peak-to-Valley value, referred to herein as “PV₉₅”, may be        obtained from the frequency distribution of positive and        negative surface heights as a function of surface height        referenced to the mean surface plane. The value PV₉₅ is the        peak-to-valley height difference which envelops 95% of the        peak-to-valley surface height data in the distribution curve by        omitting the highest and lowest 2.5% of datapoints. The PV₉₅        parameter provides a statistically significant measure of the        overall peak-to-valley spread of surface heights.-   (vii) Oxygen transmission rate can be measured using ASTM D3985.-   (viii) Water vapour transmission rate can be measured using ASTM    F1249.

The invention is further illustrated by the following examples. It willbe appreciated that the examples are for illustrative purposes only andare not intended to limit the invention as described above. Modificationof detail may be made without departing from the scope of the invention.

EXAMPLES Example 1

Dimethyl naphthalate was reacted with ethylene glycol in the presence of400 ppm manganese acetate tetrahydrate catalyst to givebis-(2-hydroxyethyl)naphthalate and low oligomers thereof, in a standardester interchange reaction. At the end of the ester interchange reaction0.025% of phosphoric acid stabiliser was added, followed by 0.04% ofantimony trioxide polycondensation catalyst. A standard batchpolycondensation reaction was performed until the intrinsic viscosity(IV) of the polyethylene naphthalate (referred to herein as “PolyesterA”) was approximately 0.50-0.575 (true PEN IV; PET equivalent IV0.75-0.85)

The polymer composition was then extruded and cast onto a hot rotatingpolished drum. The film was then fed to a forward draw unit where it wasstretched over a series of temperature-controlled rollers in thedirection of extrusion to approximately 3.34 times its originaldimensions. The draw temperature was approximately 133° C. The film wasthen passed into a stenter oven at a temperature of 138° C. where thefilm was stretched in the sideways direction to approximately 4.0 timesits original dimensions. The biaxially stretched film was then heat-setat temperatures up to about 238° C. by conventional means before beingcooled and wound onto reels. The total film thickness was 125 μm.

The heat-set biaxially stretched film was then unwound and passedthrough a series of four flotation ovens and allowed to relax byapplying the minimum line tension compatible with controlling thetransport of the web. The heat-stabilised film was then wound up. Eachof the four ovens had three controlled temperature zones in thetransverse direction (left, centre and right):

Left Centre Right Oven 1 200 213 200 Oven 2 200 213 200 Oven 3 200 213200 Oven 4 195 213 195

The line speed of the film during the heat-stabilisation step was 15m/min. The tensions used for the film (1360 mm original roll width) were24-25N.

Example 2

Dimethyl naphthalate was reacted with ethylene glycol (2.1:1glycol:ester mole ratio) in the presence of 400 ppm manganese acetatecatalyst to give bis-(2-hydroxyethyl) naphthalate and low oligomersthereof, in a standard ester interchange reaction. At the end of theester interchange reaction 0.025% of phosphoric acid stabiliser wasadded, followed by 0.020% of germanium dioxide polycondensation catalyst(133 ppm Ge metal). A standard batch polycondensation reaction wasperformed until the intrinsic viscosity (IV) of the polyethylenenaphthalate (referred to herein as “Polyester B”) was approximately0.50-0.575 (true PEN IV; PET equivalent IV 0.75-0.85). A film was thenproduced in accordance with the procedure of Example 1.

Example 3

The film of Example 2 was coated, between the forwards and sidewaysstretches during film manufacture, with a first coating compositioncomprising

-   (i) an 18% solids aqueous dispersion of a copolymer of ethyl    acrylate (EA; 48 mole %), methyl methacrylate (MMA; 48 mole %) and    methacrylamide (MA; 4 mole %) (derived from AC201®; Rohm and Haas);    18 liters-   (ii) SYNPERONIC NP10® (Uniqema; a nonyl phenol ethoxylated    surfactant; 100 ml-   (iii) 20% ammonium nitrate (20% aqueous solution); 300 ml-   (iv) Distilled water, 81 liters.

The dry thickness of the primer coating was 30 nm.

The film was then coated off-line with a second coating compositionobtained as follows:

-   (i) 517 cm³ of methyltrimethoxysilane (obtained from OSi    Specialities) was added to 1034 cm³ demineralised water at room    temperature and stirred for 24 hours.-   (ii) 54 cm³ of 3-glycidoxypropyl trimethoxysilane (obtained from    Aldrich Chemical Company) was added to 108 cm³ of demineralised    water at room temperature and stirred for 24 hours.-   (iii) 53 cm³ of 10% aqueous acetic acid (Aldrich Chemical Company)    was added to 700 cm³ of Ludox LS colloidal silica (12 nm). To this    was added 162 cm³ of the hydrolysed 3-glycidoxypropyl    trimethoxysilane/water mixture and 1551 cm³ of the hydrolysed    methyltrimethoxysilane/water mixture. This mixture was stirred for    12 hours before coating. The final pH of the composition was 6.05.    The thickness of the coating was 2.3±0.2 μm.

Example 4

The procedure of Example 3 was repeated, except that the second coatingcomposition was applied to give a coat thickness of 4.6±0.2 μm

The surface roughness of the films of Examples 1 to 3 is shown in Table1.

TABLE 1 Surface Roughness Ex. 1 Ex. 2 Ex. 3 Ra (nm) 0.64 0.63 0.58 Rq(nm) 0.90 0.82 0.74

The results in Table 1 show that a superior smoothness is obtained forExample 3.

The planarising effect is also illustrated by inspection of FIG. 1,which shows the number of extreme surface peaks greater than 200 nm.Curve (3) in FIG. 1 was obtained by analysis of Example 3 beforeapplication of the second coating composition. Curve (2) was obtained byanalysis of Example 3 after application of the second coatingcomposition. Curve (1) was obtained by analysis of Example 4. TheN(300-600) values for the curves shown is FIG. 1 are 250, 31 and 8 forcurve 3, curve 2 and curve 1, respectively. Thus, the reduction F is 8for curve 2 and 31 for curve 1.

Example 5

Dimethyl naphthalate was reacted with ethylene glycol in the presence of210 ppm manganese acetate tetrahydrate catalyst to givebis-(2-hydroxyethyl)naphthalate and low oligomers thereof, in a standardester interchange reaction. At the end of the ester interchange reaction0.025 wt % of phosphoric acid stabiliser was added, followed by 0.036 wt% of antimony trioxide polycondensation catalyst. A standard batchpolycondensation reaction was performed.

The polymer composition was extruded and cast onto a hot rotatingpolished drum. The film was then fed to a forward draw unit where it wasstretched over a series of temperature-controlled rollers in thedirection of extrusion to approximately 3.1 times its originaldimensions. The draw temperature was approximately 145° C. The film wasthen passed into a stenter oven at a temperature of 145° C. where thefilm was stretched in the sideways direction to approximately 3.5 timesits original dimensions. The biaxially stretched film was then heat-setat temperatures up to about 240° C. by conventional means before beingcooled and wound onto reels. The total film thickness was 125 μm. Thefilm was then heat-stabilised as described for Example 1.

Example 6

The procedure of Example 5 was followed except that an aqueous primercoating composition was coated between the forward and sidewaysstretching steps onto the substrate to give a coat thickness of 50 nm.The primer coating had the following solids content:

-   (i) 67% of a copolyester emulsion (wherein the acidic components of    the copolyester comprise 65 mol % of 2,6-naphthalenedicarboxylic    acid, 30 mol % of isophthalic acid and 5 mol % of 5-sodium    sulfoisophthalic acid, and the glycol components comprise 90 mol %    of ethylene glycol and 10 mol % of diethylene glycol; Tg=80° C.;    average molecular weight=13,000; produced in accordance with a    method described in Example 1 of JP-A-116487/1994);-   (ii) 20% of an aqueous dispersion of an acrylic resin (comprising 30    mol % of methyl methacrylate, 30 mol % of 2-isopropenyl-2-oxazoline,    10 mol % of polyethylene oxide (n=10) methacrylate and 30 mol % of    acrylamide; Tg=50° C.; produced in accordance with a method    described in Production Examples 1 to 3 of JP-A-37167/1988).-   (iii) 3% inert particles (silica and SiO₂—TiO₂; average particle    diameter in the range of 40 to 120 nm)-   (iv) 5% carnauba wax-   (v) 5% polyoxyethylene (n=7) lauryl ether

Example 7

The procedure of Example 6 was followed and then the film coatedoff-line with the planarising coating composition of Example 3. Thethickness of the planarising coating was 2.8 μm±0.2 μm.

TABLE 2 Surface Roughness Ex. 5 Ex. 6 Ex. 7 Ra (nm) 0.70 1.77 0.47 Rq(nm) 1.11 2.98 0.62 Peak: Valley value PV₉₅ (nm) 3.47 8.75 2.28 SurfaceArea Index — 1.000024 1.000003 Rp (Standard deviation) 68.1 (39.8) 131.8(20.7) 17.7 (8.2)

A comparison of the surface area index of Examples 6 and 7 indicate thatthe surface of Example 7 is about 8 times smoother than that of Example6.

1. A method of improving the surface smoothness of a polymericsubstrate, comprising disposing a coating layer on a surface of thepolymeric substrate by a process comprising applying to a surface of thepolymeric substrate a coating composition comprising: (a) from about 5to about 50 weight percent solids, the solids comprising from about 10to about 70 weight percent silica and from about 90 to about 30 weightpercent of a partially polymerized organic silanol of the generalformula RSi(OH)₃, wherein R is selected from methyl and up to about 40%of the R groups are a group selected from the group consisting of vinyl,phenyl, gamma-glycidoxypropyl, and gamma-methacryloxypropyl, and (b)from about 95 to about 50 weight percent solvent, the solvent comprisingfrom about 10 to about 90 weight percent water and from about 90 toabout 10 weight percent lower aliphatic alcohol, wherein the coatingcomposition has a pH of from about 3.0 to about 8.0 and wherein asurface of said coating layer exhibits an Ra value of less than 0.6 nm,and/or an Rq value of less than 0.8 nm.
 2. The method according to claim1 wherein the pH of the coating composition is in the range 3.0 to 6.5.3. The method according to claim 1 wherein the pH of the coatingcomposition is about 6.0.
 4. The method according to claim 1 whereinsaid polymeric substrate is a polyester film.
 5. The method according toclaim 4 wherein said polymeric substrate is a poly(ethylene naphthalate)or poly(ethylene terephthalate) film.
 6. The method according to claim 4wherein the polyester is derived from 2,6-naphthalenedicarboxylic acid.7. The method according to claim 6 wherein the polyester ispoly(ethylene naphthalate) having an intrinsic viscosity of 0.5-1.5. 8.The method according to claim 1 wherein said polymeric substrate is aheat-stabilised, heat-set, oriented film.
 9. The method according toclaim 1 wherein said polymeric substrate has a shrinkage at 30 mins at230° C. of less than 1%.
 10. The method according to claim 1 whereinsaid polymeric substrate has a residual dimensional change ΔL_(r)measured at 25° C. before and after heating the substrate from 8° C. to200° C. and then cooling to 8° C., of less than 0.75% of the originaldimension.
 11. The method according to claim 1 wherein said polymericsubstrate is a heat-stabilised, heat-set, oriented film comprisingpoly(ethylene naphthalate) film having a coefficient of linear thermalexpansion (CLTE) within the temperature range from −40° C. to +100° C.of less than 40×10⁻⁶/° C.
 12. The method according to claim 1 whereinsaid substrate has a % of scattered visible light (haze) of <1.5%. 13.The method according to claim 1 wherein said substrate is aheat-stabilised biaxially oriented film.
 14. The method according toclaim 1 wherein the substrate is part of an electronic oropto-electronic device containing a conjugated conductive polymer. 15.The method according to claim 14 wherein said electronic oropto-electronic device is an electroluminescent display device.
 16. Themethod according to claim 14 wherein said electronic or opto-electronicdevice is an organic light emitting display (OLED) device.
 17. Acomposite film comprising a heat-stabilised, heat-set, orientedpolyester substrate and a coating layer, wherein the coating layer isderived from the coating composition recited in claim 1, and wherein asurface of said coating layer exhibits an Ra value of less than 0.6 nm,and/or an Rq value of less than 0.8 nm.
 18. The composite film accordingto claim 17 wherein said polyester substrate is a poly(ethylenenaphthalate) film.
 19. The composite film according to claim 17 whereinsaid polyester substrate exhibits one or more of the followingcharacteristics: (i) a shrinkage at 30 mins at 230° C. of less than 1%;and/or (ii) a residual dimensional change ΔL_(r) measured at 25° C.before and after heating the polyester substrate from 8° C. to 200° C.and then cooling to 8° C., of less than 0.75% of the original dimension;and/or (iii) a coefficient of linear thermal expansion (CLTE) within thetemperature range from −40° C. to +100° C. of less than 40×10⁻⁶/° C.;and/or (iv) a % of scattered visible light (haze) of <1.5%.
 20. Thecomposite film according to claim 17 further comprising a barrier layer.21. The composite film according to claim 20 which exhibits a watervapour transmission rate of less than 10⁻⁶g/m^(2/)day and/or an oxygentransmission rate of less than 10⁻⁵/mL/m²/day.